The purification of gases generally, including gases such as nitrogen, argon, helium, and carbon dioxide, has progressed to the point where gas purity of 99+% is routine, and 99.9+% is not uncommon. Yet, even as increasingly pure gases are made available, there are increased needs for ever purer gases; purity begets still higher levels of purity.
One area of need is the removal of sulfur-containing compounds from gases to residual levels measured in parts per billion and even lower. For example, catalyst systems employing nickel, platinum, palladium, and so forth are quite sensitive to sulfur levels, and processes employing such metals as catalysts or components of catalyst systems generally utilize a guard bed of a suitable adsorbent to remove the offending compounds. Analytical measurements also may depend upon the removal of sulfur compounds to unprecedentedly low levels for high precision and high accuracy in measurement. For example, in the case of sulfur chemiluminescence, the lower limits of instrumental detection are dependent upon the background sulfur levels in the gas supplied to the system. Removal of sulfur-containing species can dramatically improve detection levels and serves as an incentive for advanced purification methods.
We have developed a sequence of adsorbent beds employing several different adsorptive compounds to achieve a very efficient removal of sulfur-containing compounds, halocarbons, and fluorocarbons. The traditional method of removing sulfur has employed a high nickel content catalyst as a guard bed acting as a general adsorbent, including the function of nickel as a chemisorbent for sulfur-containing compounds. The multiple bed approach of our invention provides a sulfur trap with a combination of capacity and efficiency that is not achievable in other sulfur-removing technologies. Furthermore, the multiple bed approach has the added benefit of removing halocarbons.